Biology: the emergence of biological form ontogeny "development of an individual," 1872, coined from Gk. on (gen. ontos) "being" (prp. of einai "to be") + -geneia "origin," from -genes "born." Genotype Development Phenotype Preformationism: the homunculus Development consisted of an unfolding of a preformed, miniature adult. All that was required was the woman’s womb as an incubation chamber. what is one immediate theoretical problem with this idea? infinite regress An infinite regress in a series of propositions arises if the truth of proposition P1 requires the support of proposition P2, and for any proposition in the series Pn, the truth of Pn requires the support of the truth of Pn+1. There would never be adequate support for P1, because the infinite sequence needed to provide such support could not be completed. What is development? embryos and more: the life cycle concept. Gametogenesis Formation of eggs and sperm Fertilization Self explanatory, but lots going on.. Cleavage and cleavage patterns Mitosis without growth, Axis and cell fate specification Which end is up? How do cells know what to become? What genes are involved? How do cells communication with each other? Cell lineage and fate maps What they are and how they are used. Gastrulation How to make a gut and a multilayered embryo Neurulation Formation of the nervous system, with consideration of the neural crest Organogenesis Formation of organs from rudiments: eyes, limbs etc. Differentiation and Stem Cells The end game: making the cells that do the work. Differentiation and Stem Cells The end game: making the cells that do the work. And stem cells: the future of medicine? Indirect life cycles & metamorphosis Complex life cycles means having two somewhat separate developmental programs that must be linked by a metamorphosis. Special topics: Regeneration, Apoptosis preformationism vs. epigenesis epigenesis = upon formation • on theoretical grounds, epigenesis was more like another way to think about epigenesis is the progression from a less to a more differentiated state • the “cell theory” meant that all living things were composed of cells and that cells could only arise by division of already existing cells. Argued against preformationism. • among sexually reproducing organisms, germ cells are the only ones that give rise to new organisms. In the 1840s, it was recognized that the egg itself is a single specialized cell. • In 1876, using the sea urchin Toxopneustes lividus Hertwig observed a sperm entering into an egg during fertilization. Gametogenesis • how to make eggs and sperm. Fertilization • egg and sperm unite! • many biochemical reactions happen: acrosome reaction, slow/fast block to polyspermy (why is polysperm bad?), change to membrane properties, initiation of cortical rotations etc. • sperm:egg interactions and bindin (perhaps save for evo-devo?) • meiotic reduction and polar bodies. • cleavage is the mechanism by which a Cleavage: divide and single cell returns to a multicellular organism. mobilize • embryonic cleavage is different than regular mitosis in that it is rapid, involves no cell growth and usually omits the gap phases. Lots of different critters cleave in different ways: go over the main types of cleavage • cleavage is not just about dividing up the embryo: cleavage planes are the principal mechanisms by which maternal determinants are sequestered into particular lineages. Maternal • The egg is a highly specialized cell with Determinants anisotropically distributed “determinants” • it is the unequal distribution of these determinants that are responsible for cell autonomous fate specification and unequal cell divisions. • what are they? RNA/protein • use the bicoid example: start with flies, move to squirts (whittakers experiments) • move to the concept of the organizer. Cell fate specification/axis formation/patterning. • axis formation is the formation fo the basic body features and where they will occur • specification is a transcriptional state that a cell enters into: cell autonomous or conditional. only two types. • fate of specified cells can be altered experimentally. difference between specified and committed or determined. • Hox genes. Cell lineage/fate maps • why there are useful and how they are created. • general labelling techniques and how they are used. • a central concept: intercellular Induction/pattern formation communication • can happen in three ways: diffusion (morphogen); direct contact (transmembrane proteins) or gap junctions (coupling). • induction causes new gene transcription and change in the development of the induced cell. • permissive vs. instructive inductions and the issue of competence. • lateral inhibition Gastrulation • the concept of germ layers • the formation of the gut, all embryos go through this stage • It is neither birth, marriage nor death, but gastrulation which is truly the most important time of your life. many things are happening. • maternal/zygotic transitions. • talk about different gastrulation mechanisms (tissue level) as well as the cytoskeleton. Neurulation • Formation of the nervous system in vertebrates • neural crest as a major innovation. • neurocristopathies. • synapse formation averts the death signal. Organogenesis • epithelial mesenchymal interactions as the fundamental basis of organogenesis. • select a couple of models like limb formation, heart formation, eye formation, tooth formation where there are multiple tissue interactions. • what makes a differentiated cell? Really Differentiation/Stem cells a continuation of embryogenesis, but irreversible restriction of developmental potential (except in the case of regeneration). • models of cell differentiation (with respect to locking in patterns of gene transcription. • differentiated cell is characterized by the proteins it contains, and consequently the function in performs (could reverse these) • use the myoD example for fibroblasts. Germ cells: where do they come from? • insert pic of germ/somatic cell distinction • different cells do it differently: germ line specification (vasa) and early segregation vs. genital ridge and inductive interactions. Indirect life cycles • metamorphosis in frogs/flies/sea urchins. • the role of hormones in co-ordinating multiple developmental events. Special topics: • regeneration. • apoptosis. • stem cell cloning technologies.
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